Apparatus for generating atmospheres are known, in particular atmospheres for heat-treating metals, and in particular atmospheres referred to as "protective". The treatments in question are, in particular, annealing, tensuring, pre-quench heating, decarburizing, brazing or sintering. An atmosphere of this type comprises predominantly nitrogen and controlled levels of reducing or carburizing, and oxidizing or decarburizing species.
These atmospheres are generally produced by a reactor which incompletely combusts a hydrocarbon, for example natural gas, with a nitrogen-rich oxidant gas, for example air or alternatively impure nitrogen having some residual oxygen level (most often in excess of 0.5%).
A method of obtaining a heat-treatment atmosphere employing a catalytic reaction of this type is described, for example, in EP-B-0,482,992.
Apparatus for generating atmospheres traditionally include control loops which employ means for measuring at least one parameter representing the actual operation of the apparatus. These means are connected to means for processing the values measured. They are formed by controllers which, for example, act on the temperature of the reactor or the inlet flow rates of the combustible and oxidant gases.
Apparatus equipped with control loops of this type operate properly in steady state. However, the control loops do not make it possible to guarantee the quality of the atmosphere produced in the event of serious drifts in certain parameters. In particular, the control loops cannot provide sufficient correction to remedy the premature aging of the catalytic mass contained in the reactor, or other components of the apparatus.
Thus, the user may not observe the degradation of certain elements of the apparatus until late, even though the quality of the atmosphere which is produced has already become unsatisfactory.
The means currently employed for atmosphere generation apparatus do not make it possible to predict future failures. Thus, there is an inability of control loops to compensate for these failures. Consequently, the progressive deterioration of the apparatus inevitably leads to its being stopped when it produces an atmosphere whose quality does not meet specifications. This shutdown frequently causes significant production losses in the downstream device which uses the atmosphere.
Further, before becoming able to observe the degradation in the quality of the atmosphere which is produced, the user device located downstream will continue to fabricate or treat products which need to be destroyed since they do not satisfy the requisite quality criteria.
The use of such atmosphere generation apparatus thus leads to significant extra costs when they age.
Further, the complexity of the atmosphere generation methods employed in these apparatus makes it very difficult to implement an efficient program for preventive maintenance. Indeed, calculation of the lifetime of the various constituents involves a high degree of complexity.
Users currently resort to changing the constituents of the generation apparatus frequently, even though they quite often do not require such replacement. This approach consequently entails high costs for operating this type of apparatus.